most of your problems are DNS related without at least SPF setup in DNS and no reverse DNS records so nothing to do with default Centmin Mod postfix setup

see

You're not fully authenticated
We check if the server you are sending from is authenticated
-1[SPF] server.rockraidersunited.com does not allow your server 198.204.226.194 to use [email protected]
Sender Policy Framework (SPF) is an email validation system designed to prevent email spam by detecting email spoofing, a common vulnerability, by verifying sender IP addresses.
You do not have a SPF record, please add the following one to your domain server.rockraidersunited.com:

v=spf1 a mx ip4:198.204.226.194 ~allNeed guidance?View guides for each host.

-1[Sender ID] rockraidersunited.org does not allow your server 198.204.226.194 to use [email protected]
Sender ID is like SPF, but it checks the FROM address, not the bounce address.
What we retained as your current SPF record is:

v=spf1 +a +mx +ip4:216.97.239.65 ?all
You have ?all in your SPF, instead of ~all. This means we can't verify if your SPF is good, although it might probably be!

-1Your message is not signed with DKIM
DomainKeys Identified Mail (DKIM) is a method for associating a domain name to an email message, thereby allowing a person, role, or organization to claim some responsibility for the message.

Your reverse DNS does not match with your sending domain.
Reverse DNS lookup or reverse DNS resolution (rDNS) is the determination of a domain name that is associated with a given IP address.
Some companies such as AOL will reject any message sent from a server without rDNS, so you must ensure that you have one.
You cannot associate more than one domain name with a single IP address.

Your IP address 198.204.226.194 is associated with the domain rockraidersunited.com.
Nevertheless your message appears to be sent from server.rockraidersunited.com.

You may want to publish a pointer (PTR type) DNS record with a value of server.rockraidersunited.com or use rockraidersunited.com as hostname in your mail software